A reliability evaluation method of ion thruster was established under the situation that only two ion thrusters were tested and the results were represented by very few failure data. Meanwhile

the significant test information from the last failure data test to non-occurrence of failure was fully developed by introducing the concept of interval statistic. Best linear unbiased point estimator of the life distribution parameters was calculated by using Gauss-Markov theorem. And then the one-side lower confidence limits of reliability and life were given. At last

while evaluating the reliability of NASA's XIPS-13 ion thrusters

the one-side lower confidence limits of the reliability with the demanding lifetime 10000h was 0.87 and the one-side lower confidence limits of the lifetime with a given reliability 0.9 was 9024.6h. It demonstrates that this method has high accuracy and can be easily applied in engineering.